Shared mesh signaling method and apparatus

ABSTRACT

In a mesh network, a network element for providing protection switching in a 1:N shared mesh protection scheme having a first protection path associated with a pair of working paths selected from the N working paths is disclosed. The network element comprising: (a) a link for connecting the network element to a first working path of the pair of working paths in a path layer of the network, the path layer including a plurality of interconnected network elements; (b) a routing table accessible by the network element, the routing table for having local protection channel information associated with a local protection segment separate from the first protection path, the local protection segment connecting the network element and one of the interconnected network elements adjacent to the network element; and (c) an identification module for using the local protection channel information to identify an available protection channel on the local protection segment in the event of failure of a local working segment of the first working path, the local working segment connecting the network element and said one of the adjacent interconnected network elements; wherein the available local protection channel on the local protection segment is used to switch local network bandwidth from the failed local working segment to the local protection segment after the failure has been detected. Selection functions are also disclosed.

This is a continuation of U.S. patent application Ser. No. 10/059,344,filed Jan. 31, 2002 now U.S. Pat. No. 6,917,759

The present invention relates to optical communication systems and, inparticular, to apparatus and methods for providing protection signalingbetween network elements.

BACKGROUND OF THE INVENTION

Optical communication systems have become widely implemented in todaystelecommunication networks. The Synchronous Optical Network (SONET) is astandard for Synchronous Telecommunication Signals used for opticaltransmission based on the synchronous digital hierarchy (SDH). SONET canprovide the ability to combine and consolidate traffic through grooming,and can reduce the amount of back to back multiplexing in providingtransport services for ATM, SMDS, and Frame Relay, etc. Furthermore,network providers can use SONET network features to reduce the operationcosts of the transmission network. The next generation of opticalnetworks may be the optical transport network (OTN) standard.

The network standards are ANSI T1.105 for SDH and Bellcore GR-253-COREfor SONET, which define the physical interface and optical line rateknown as the optical carrier (OC) signals, a frame format, and an OAMProtocol. In operation of the SONET system, user signals are convertedinto a standard electrical format called the Synchronous TransportSignal (STS), which is the equivalent of the optical signal. A singleoptical channel operates and transmits data according to a high speedsynchronous digital hierarchy standards, such as the SONET OC-3, OC-12,and OC-48 rate protocols, which carry rates equivalent to tens ofthousands of voice calls. Accordingly, it is critical in todays opticalcommunication systems to provide and maintain the integrity of datacommunication networks even during problem time periods, due to thelarge number of transmissions that can be interrupted.

The increased capacity of optical fibre has raised concerns about thereliability and survivability of an optical network, since a singlecable cut or equivalent malfunction can impact a large amount of datatraffic. Cable cuts can be frequent and almost impossible to avoid,caused by human error or inclement weather. Furthermore, equipmentfailures resulting from man made or natural disasters are additionalpossibilities. Accordingly, optimized protection signaling systems andmethods are desired in order to quickly re-establish networkcommunications once failures have been detected.

Two types of failures can be experienced in a telecommunication network,such as line failures and module failures. The basic telecommunicationnetwork structure consists of various links situated betweencorresponding transmitters and receivers, which are also referred to asmodules. Accordingly, a line failure can include damage to the physicalfibre and optical components, such as the malfunction of amplificationequipment situated along the optical data path. In contrast, the modulefailure can consist of the transmission or reception equipment, such asa laser diode transmitter. It should be noted that both line failuresand module failures may disable the network segment or link between twoadjacent nodes. It is therefore required in todays telecommunicationnetwork systems to provide restoration techniques to restore theinterrupted traffic temporarily until the detected failure is repaired.One such protection system currently in use is line protection.

One known line protection system is Bi-direction Line Switched Ringsystems (BLSR), which have the advantage of relatively fast speedprotection circuitry. These ring systems consist of a plurality of nodescoupled in a ring by two multiplexed communication paths, which providedata transmission in opposite directions around the ring. In thepresence of a fault such as a fibre cut, the BLSR system detects thepresence of this failure in the two nodes immediately adjacent the faultand the communications are maintained via both paths forming the closedloop. The communication signals are therefore transmitted along the twopaths from the two nodes adjacent to the fault. The BLSRs are currentlyused in Backbone networks and are therefore built for higher datatransfer rates such as the OC-12/48 Further BLSR protection systems caninclude 4F and 2F implementations.

One disadvantage with BLSR systems is that they can not be easilyapplied to already existing (synchronous or asynchronous) communicationsystems without requiring costly equipment upgrades, for example achange in wavelength or bit rate involves a change in equipment. Inaddition, BLSR systems have disadvantages in that they do not providefor 1:N protection (i.e. protection of N working paths using at leastone shared protection link) since path deployment is typicallydesignated as 50% working and 50% protection, however as BLSR does notsupport Timeslot Interchange (TSI), the actual efficiency of the workingbandwidth is about three quarters of the designated 50% deployment.Furthermore, BLSR systems can have an additional limitation that allnodes around the ring must be of the same type and must have the samecapacity

One technique that has been tried in order to remove the problems of theBLSR design is a mesh protection design. In a full mesh design, eachnetwork element within a network is coupled to every other networkelement. On a partial mesh design, less optical carrier links areutilized. Well known mesh techniques have an advantage in terms ofminimising the requirements for dedicated protection link bandwidth,since the optical bandwidth used for protection is only assigned to aprotection link (or protection path having a series of links) during afailure situation, hence reducing the cost of additional fibre andproviding greater network flexibility. However, one key problem withthese well known mesh designs is the amount of time that is required tolocate and establish the required protection link and a subsequent newworking path after a failure occurs. The time it takes to re-establishcommunications after failure is critical since the time period duringprotection switching and protection link establishment should be smallenough so as to practically unnoticeable the devices or peopletransmitting/receiving the data traffic. These systems typically use thecontrol layer of the network to assist in protection switching, whichcan provide undesirable protection switching times on the order ofseconds. Accordingly, alternative protection signaling systems andmethods are desired to potentially reduce the switching times by anorder of magnitude.

A further solution to address the desirability of fast protection timesis to provide switching at the line level between adjacent networkelements. This type of system could probably provide times in the 50msec range, however would require protection bandwidth to be madeavailable between every network element which would add to thecomplexity of the network architecture. Another solution could be to usethe signaling network to do the switching, which could provideflexibility of sharing bandwidth between adjacent network elements.However, this method of using the signaling network has a disadvantagedue to the processing of network overhead, whereby desirable protectiontimes of less than 300 msec may not be achievable consistently.Accordingly, alternative protection signaling systems and methods aredesired to reduce switching times, without substantially increasingnetwork architecture and/or overhead processing.

A further disadvantage of present mesh protection schemes is that once ashared protection link is assigned to help provide protection backup toa particular working path, the remaining working paths associated withthe shared protection link typically become unprotected. The process ofimplementing nodal/path diversity for the mesh network can helpalleviate some of the risk involved with using a shared protection linkbetween multiple working paths. However, there is a possibility of twounrelated failures occurring on separate working paths, therebyresulting in the undesirable situation of the two working pathscompeting to acquire usage of the one common shared protection link.

Another disadvantage of current mesh protection schemes is that bothworking paths and protection paths (having a plurality of protectionlinks) are defined from the source node to the termination node.Therefore, once selected, the entire protection pathway consisting ofmultiple protection channels or timeslots is assigned to accommodate anytransmissions originally destined over the failed working path. Thissymmetrical assignment of protection capacity can result in aninefficient use of available bandwidth on the protection path, as someof the protection capacity assigned is typically not used by the trafficdemands when transferred from the failed working path.

It is an object of the present invention to provide a protectionsignaling system in a shared mesh environment to obviate or mitigatesome of the above-presented disadvantages.

SUMMARY OF THE INVENTION

The present invention is directed to both local and globalimplementations of a shared mesh protection scheme for defining anassociated protection link when a working connection is established. Theshared protection link is used to help protect data traffic in workingpaths, in the event a network failure of the working paths is detectedin a mesh network. Currently, there are flexibility, bandwidthefficiency, and undesirable set-up period problems with existing meshprotection schemes. In the present invention, during implementation ofthe global protection scheme, the corresponding protection pathinformation is sent down to switch cards of network elements making upthe protection path, which consists of a series of protection linksincluding one or more shared protection links. It is recognized that theprotection path can be composed of one shared protection link. Theprotection path information is contained within interrupt drivenoverhead bytes to provide for failure detection and protection pathset-up in a path layer of the mesh network.

Upon detection of the failure, the network elements use overhead bytemessages to implement local protection switching and switch selection onan available local protection segment or link. In the event localprotection switching is not available, global protection switching canuse a particular overhead byte message format to inform the routingsource network element of the failure in the working path. The messagescontain a failure indicator. The routing source network element sendsthe corresponding overhead byte messages down the defined protectionpath to provide for protection path establishment according to preloadeddata associated with the switch cards of the affected network elements.This preloaded data is contained in a routing table that is locallyaccessible by the network elements in the path layer. Once the failurehas occurred and has been indicated to a source network element, thesource element sends protection signaling messages using the overheadbytes to the corresponding network elements along the protection path.Accordingly, the routing tables located at the switch cards of thenetwork elements, set-up when the working path connections wereinitially established, determine this dynamically allocated protectionpath environment. Therefore, based on the information contained in thesetables, the actual protection path is established upon receiving the ACKfrom the termination node of the failed working path transmitted alongthe now established protection path. It is noted that interrupt drivenoverhead bytes for network traffic are used to provide for protectiontimes of less than 300 msec.

According to the present invention there is provided a network elementfor providing protection switching in a 1:N shared mesh protectionscheme having a first protection link associated with a pair of workingpaths. The network element comprises: a link for connecting the networkelement to a first working path of the pair of working paths selectedfrom the N working paths in a path layer of the network, the path layeradapted to include a plurality of interconnected network elements forproviding the first protection link associated with the pair of workingpaths, a routing table accessible by the network element, the routingtable for having local protection channel information associated with alocal protection segment separate from the first protection link, thelocal protection segment adapted to connect the network element and oneof the interconnected network elements adjacent to the network element;and an identification module for using the local protection channelinformation to identify an available protection channel on the localprotection segment in the event of failure of a local working segment ofthe first working path, the local working segment adapted to connect thenetwork element and the one of the adjacent interconnected networkelements; wherein the available local protection channel on the localprotection segment is used to switch local network bandwidth from thefailed local working segment to the available local protection segmentafter the network failure has been detected.

According to a further aspect of the present invention there is provideda method for providing protection switching in a 1:N shared meshprotection scheme having a first protection link associated with a pairof working paths. The method comprises the steps of interconnecting anetwork element to a first working path of the pair of working pathsselected from the N working paths in a path layer of the network, thepath layer adapted to include a plurality of interconnected networkelements for providing the first protection link associated with the Nworking paths, defining a routing table accessible by the networkelement, the routing table having local protection channel informationassociated with a local protection segment separate from the firstprotection link, the local protection segment connecting the networkelement and one of the interconnected network elements adjacent to thenetwork element; identifying by the network element a failure of a localworking segment of the first working path, the local working segmentconnecting the network element and the one of the adjacentinterconnected network elements; using the local protection channelinformation by the network element to identify an available protectionchannel on the local protection segment; and switching local networkbandwidth from the failed local working segment to the available localprotection channel on the local protection segment.

According to a still further aspect of the present invention there isprovided a computer program product for providing protection switchingin a 1:N shared mesh protection scheme having a first protection linkassociated with a pair of working paths. The product comprises computerreadable medium; a first link module stored on the computer readablemedium for connecting a network element to a first working path of thepair of working paths selected from the N working paths in a path layerof the network, the path layer adapted to include a plurality ofinterconnected network elements for providing the first protection linkassociated with the pair of working paths; a routing module stored onthe computer readable medium and accessible by the network element, therouting module for storing local protection channel informationassociated with a local protection segment separate from the firstprotection link, the local protection segment adapted to connect thenetwork element and one of the interconnected network elements adjacentto the network element; and an identification module coupled to therouting module, the identification module for using the local protectionchannel information to identify an available protection channel on thelocal protection segment in the event of failure of a local workingsegment of the first working path, the local working segment adapted toconnect the network element and the one of the adjacent interconnectednetwork elements; wherein the available local protection channel on thelocal protection segment is used to switch local network bandwidth fromthe failed local working segment to the available local protectionsegment after the network failure has been detected.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the preferred embodiments of the inventionwill become more apparent in the following detailed description in whichreference is made to the appended drawings wherein.

FIG. 1 is a diagram of a data communication network,

FIG. 2 is a sub-network of the network of FIG. 1;

FIG. 3 a shows an STS-1 frame format,

FIG. 3 b shows further detail of the frame format of FIG. 3 a;

FIG. 4 a is a protection signaling scheme on the sub-network of FIG. 2;

FIG. 4 b shows connection maps for the sub-network of FIG. 4 a,

FIG. 4 c shows routing maps of the protection signaling scheme for thesub-network of FIG. 4 a;

FIG. 5 shows a failure mode for an alternative embodiment of thesub-network of FIG. 4 a,

FIG. 6 is an operational flowchart of the sub-network of FIG. 4 a;

FIG. 7 is a further operational flowchart of the sub-network of FIG. 4a;

FIG. 8 is a further embodiment of the sub-network of FIG. 5,

FIG. 9 shows a failure mode for the sub-network of FIG. 8, and

FIG. 10 is an operational flowchart of the sub-network of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a global telecommunication network 10 contains aseries of sub-networks An, Bn, Cn, Dn, En interconnected by bulk datatransmission mediums 12. These mediums 12 can consist of such as but notlimited to optical fibre, wireless, and copper lines which arecollectively referred to as the Backbone Network. Each sub-network An,Bn, Cn, Dn, En contains a plurality of network elements 14interconnected by conduits 16, which can be collectively referred to aspath layer 17 (see FIG. 2). These conduits 16 can consist of fibre opticcables, DSL (Digital Subscriber Loop), cable, and wireless mediums,wherein each conduit 16 can be capable of providing the transmission ofmultiple wavelengths 18 as required by the telecommunication network 10.The transmission structure of the telecommunication network 10 can beused by a variety of different carriers, such as ILECs, CLECs, ISPs, andother large enterprises to monitor and transmit a diverse mixture ofdata packets 20 in various formats. These formats can include voice,video, and data content transferred over the individual SONET, SDH, IP,WDN, ATM, and Ethernet networks associated with the telecommunicationnetwork 10.

Referring to FIG. 2, operation of each network element 14 can bemonitored by a central integrated management or Operations SupportSystem (OSS) 22, which for example co-ordinates a plurality ofconnection requirements 24 received from clients 26 connected to thesub-network E. Alternatively, these connection requirements 24 can alsobe communicated directly to a corresponding Optical ConnectionController (OCC) 28. The centrally integrated management or OperationsSupport System 22 can include a processor 25. The processor 25 iscoupled to a display 27 and to user input devices 23, such as akeyboard, mouse, or other suitable devices. If the display 27 is touchsensitive, then the display 27 itself can be employed as the user inputdevice 23. A computer readable storage medium 21 is coupled to theprocessor 25 for providing instructions to the processor 25 to instructand/or configure the various OCCs 28, and corresponding coupled networkelements 14, to perform steps or algorithms related to the operation ofa shared protection class of service with protection signalingimplemented on the path layer 17 of the sub-network En. The computerreadable medium 21 can include hardware and/or software such as, by wayof example only, magnetic disks, magnetic tape, optically readablemedium such as CD ROM's, and semiconductor memory such as PCMCIA cards.In each case, the medium 21 may take the form of a portable item such asa small disk, floppy diskette, cassette, or it may take the form of arelatively large or immobile item such as hard disk drive, solid statememory card, or RAM provided in the support system OSS. It should benoted that the above listed example mediums 21 can be used either aloneor in combination.

The clients 26 or other peripheral devices of the sub-network En caninclude such as but not limited to hubs, leased lines, IP, ATM, TDM,PBX, and Framed Relay PVC. Coupled to each network element 14 by link 31is the OCC 28, which co-ordinates a connection and data request 30 toeach of their corresponding network elements 14. This association ofOCCs 28 is also referred to as a control layer 15 with each OCC 28coupled together by links 32. The OCCs 28 have a complete picture oftheir corresponding element 14 interconnections.

Accordingly, the shared mesh protection class of service with protectionsignaling can be implemented on the sub-network En in regard to theco-ordination of the plurality of connection requirements 24 submittedby the clients 26, as well as monitoring the timely transmission of thedata packets 20. The shared protection class of service can include bothlocal and global protection schemes, as further described below.

The shared protection class of service provides a SONET protectionsignaling scheme for use in mesh networks. It is preferable that theprotection signaling scheme be able to provide protection or restorationtimes of less than 200 msec for a large number of network connectionsconsisting of coupled network elements 14 and OCCs 28, as furtherdescribed by way of example only. The signal transmission and receptionof data packets 20 and protection signaling 38 (see FIG. 5) over thesub-network En can be performed using the Synchronous Transport Signal(STS) frame format 200 (see FIG. 3 a), which is a basic building blockof a SONET optical interface. The following is a description of theSONET transmission format that can be used to implement the local andglobal protection signaling schemes on the path layer 17 of thesub-network En.

Referring to FIGS. 2, 3 a, and 3 b, the STS-1 (level 1) is the basicsignal rate of SONET and multiple STS-1 frames 200 may be concatenatedto form STS-N frames 200, where the individual STS-1 signals are byteinterleaved. The STS-1 frame 200 comprises two parts, the STS payload202 having 87 columns by 9 rows for a total of 783 bytes, and the STStransport header or overhead 204, having 3 columns by 9 rows for a totalof 27 bytes. It should be noted the payload 202 can also contain a pathoverhead 206 having 1 column by 9 rows for a total of 9 bytes. The STSpayload 202 carries the information portion of the STS-1 frame 200,while the STS transport overhead 204 carries the signaling and protocolinformation. This allows communication between network elements 14within the sub-network En, facilitating administration, surveillance,provisioning, and control of the sub-network En from a central location.At the ends of the sub-network En, such as the clients 26, the datapackets 20 with various rates and different formats are processed. ASONET end-to-end connection (see FIG. 4 a for example connections A-B,C-D) includes line terminating equipment at both ends, both source anddestination nodes, responsible for converting the data packets 20 fromthe user format to the STS format prior to transmission through theSONET sub-network En, and for converting the data packets 20 from STSformat back to the user format once transmission is complete.

SONET networks typically contain a four layer system hierarchy, witheach layer building on the services provided by the lower layers. Eachlayer communicates to peer equipment in the same layer, processesinformation and passes it up and down to the next layer. The path layer17 (FIG. 2) helps to provide the end-to-end transport of data packets 20converted to STS-1 payload 202 at the appropriate signaling speed,mapping services (such as DS1, DS2, DS3 and video), and path overhead206 into Synchronous Payload Envelopes (SPEs) of the STS-1 frame 200.The control layer 15 helps to multiplex and synchronize the SPEs and canadd line overhead 208 of the transport overhead 204 to form STS-Ncombined signal frames 200. The section layer (not shown) can performscrambling and framing, and can add section overhead 210, in order tocreate the STS-1 frames 200. Finally, the photonic layer (not shown) isthe SONET physical layer, converting electrical signals into opticalSTS-1 frames 200 and transmitting these to distant network elements 14.Further, at the distant network elements 14 the process is reversed,starting with the photonic layer, whereby the optical STS-1 frames 200are converted to the electrical data packets 20 and passed down throughthe path layer 17 where the different service signals terminate.Further, the optical form of the STS-1 signals are called OpticalCarriers (OCs), wherein the STS-1 signal and the OC-1 signal aredesigned to have the same rate.

It is recognized that higher rate STS-1 frames 200 can be obtained bybyte interleaving N aligned STS-1 frames 200 to form an STS-N frame 200in accordance with conventional SONET technology. An STS-N frame 200 maybe viewed as having a repetitive frame structure, wherein each frame 200comprises the transport overhead bytes 204 of N STS-1 frames 200 and Nsynchronous payload envelopes 202. For example, three STS-1 signals maybe multiplexed by a multiplexer into an STS-3 signal. The bit rate ofthe STS-3 signal is three times the bit rate of an STS-1 signal and thestructure of each frame of the STS-3 signal comprises three synchronouspayload envelopes 202 and three fields of overhead bytes 208 from thethree original STS-1 signals When transmitted using optical fibres, theSTS-N signal is converted to optical form and is designated as the OC-Nsignal. Furthermore, the protection P paths (see below) can also be OC3cup to OC192c as long as the infrastructure of the sub-network Ensupports concatenated payloads 202.

Referring to FIG. 3 b, the transport overhead 204 and path overhead 206for the STS-1 frame 200 of FIG. 3 a are described in greater detailbelow, in particular the overhead bytes that can be used in transmissionof the protection signals 38 (see FIG. 5) Selected bytes of theseoverheads 204, 206 are employed for failure identification andprotection switching for the shared mesh protection scheme implementedon the sub-network En. As noted above, the overhead bytes contained inthe overheads 204, 206 are distributed in 4 columns, each consisting of9 rows.

The overhead bytes associated with the section overhead 210 of thetransport overhead 204 include framing A1 and A2 bytes, which arededicated to each STS-1 to indicate the beginning of the STS-1 frame200. The A1, A2 bytes pattern is F628 hex (this F628 is neverscrambled). When 4 consecutive errored framing patterns have beenreceived, an OOF (Out Of Frame) condition is declared. When 2consecutive error free framing patterns have been received, an in framecondition is declared. The section overhead 210 also contains a STS-IDC1 byte, which is a number assigned to each STS-1 signal in the STS-Nframe in according to the order of its appearance, i.e. the C1 byte ofthe first STS-1 signal in the STS-N frame is set to 1, the second STS-1signal is 2 and so on. The C1 byte is assigned prior to bye interleavingand stays with the STS-1 until deinterleaving. A section BIP-8 B1 byteis allocated from the first STS-1 of the STS-N for section errormonitoring. The B1 byte is calculated over all bits of the previousSTS-N frame 200 after scrambling using a bit interleaving parity 8 codewith even parity. The B1 byte of the current STS-N frame 200 iscalculated and compared with the B1 byte received from the first STS-1of the next STS-N frame 200. If the B1 bytes match, there is no error.If the B1 bytes do not match and the threshold is reached, then an alarmindicator is set. An orderwire E1 byte is allocated from the first STS-1of the STS-N frame 200 as local orderwire channel for voice channelcommunications. Accordingly, one byte of the STS-1 frame 200 is 8bits/125 usec or 64 Kbps which is the same rate as a voice frequencysignal. A user F1 byte is set for the user purposes, and is passed fromone section level to another and terminated. A plurality of datacommunication D1, D2 and D3 bytes are allocated from the first STS-1 ofthe STS-N frame. This 192 kbps message channel of the D1, D2, D3 bytescan be used for alarms, maintenance, control, monitoring, administrationand communication needs.

The overhead bytes of the line overhead 208 of the transport overhead204 include Pointer H1 and H2 bytes, which in each of the STS-1 signalsof the STS-N frame 200 is used to indicate an offset in the bytesbetween a pointer and the first byte of the STS-1 SPE The pointer isused to align the STS-1 SPE in an STS-N signal as well as to performfrequency justification. The first pointer H1 byte contains the actualpointer to the SPE, the following pointer H2 byte contains the linkingindicator which is 10010011 11111111. The Pointer Action H3 byte in eachof the STS-1 signals of the STS-N frame 200 is used for frequencyjustification purpose Depending on the pointer value, the H3 byte isused to adjust the fill input buffers. The H3 byte only carries validinformation, but it is not defined for negative justification The BIP-8B2 byte in each of the STS-1 signal of the STS-N frame 200 is used forline error monitoring function. Similar to the B1 byte in the sectionoverhead 210, but the B2 byte uses bit interleaving parity 8 code witheven parity The byte B2 contains the result from the calculation of allthe bits of line overhead 208 and the STS-1 payload envelope 202capacity of the previous STS-1 frame 200 before scrambling The AutomaticProtection Switching (APS) K1 and K2 bytes are allocated for APSsignaling between line level entities for line level bi-directional APS.These bytes K1, K2 are defined only for STS-1 number 1 of the STS-Nsignal frame 200. The Data Communication D4-D12 bytes are allocated forline data communication and should be considered as one 576-kbpsmessage-based channel that can be used for alarms, maintenance, control,monitoring, administration, and communication needs between two sectionline terminating network elements 14. The D4-D12 bytes of the rest ofthe STS-N frame 200 are not typically defined. The Growth/FEBE Z1 and Z2bytes are set aside for functions not yet defined. The Orderwire E2 byteis allocated for orderwire between line entities. This E2 byte isdefined only for STS-1 number 1 of the STS-N signal frame 200

The overhead bytes of the path overhead 206 of the payload 202 envelopeare assigned to and transported with the payload 202 The path overhead206 is created by the PTE as part of the SPE until the payload envelope202 is demultiplexed at the destination path network elements 14. Thepath overhead 206 supports the following four classes of operation:Class A payload independent functions required by all payload type,Class B mapping dependent functions not required by all payload type,Class C application specific functions, and Class D undefined functionsreserved for future use. Accordingly, the Trace J1 byte, class A, isused by the receiving network element 14 to verify the path connectionin the sub-network En. The BIP-8 B3 byte, class A, is assigned for patherror monitoring. The path B3 byte is calculated over all bits of theprevious STS SPE before scrambling using bit interleaved parity 8 codewith even parity. The Signal Label C2 byte, class A, is assigned toindicate the construction of the STS SPE. The following hex values ofthe C2 byte has been defined as 0x00 —Unequipped signal, 0x01—Equippedsignal, 0x02—Floating VT mode, 0x03—Locked VT mode, 0x04 —Asynchronousmapping for DS3, 0x12—Asynchronous mapping for 139.264 Mbps, 0x13—Mapping for ATM, 0x14—Mapping for DQDB, and 0x15—Asynchronous mappingfor FDDI. The Path Status G1 byte, class A, is assigned to carry back anoriginating STS PTE of the path terminating status and performance. Thisallows a complete duplex path to be monitored at either end. The UserChannel F2 byte, class C, is allocated for user communications betweennetwork elements 14. The Indicator H4 byte, class C, provides ageneralized multi-frame indicator for the payload 202. The Growth 3bytes, Z3-Z5, are class D and are reserved for future functions.

As further noted below, some of the interrupt driven (i.e. consideredfast access) overhead bytes, selected from the transport overhead 204and/or the path overhead 206, are employed to implement the protectionsignaling scheme on the path layer 17 of the sub-network En It should benoted that shared protection signaling schemes for mesh networkarchitecture, in general, can include one conduit 16 between twocorresponding network elements 14 assigned as a protection P link (seeFIG. 4 a) of a 1:N group, wherein the number “1” represents the groupnumber and the letter “N” represents the particular member number of thecorresponding group “1”. Accordingly, each of the working W paths (seeFIG. 4 a) become the members of the 1:N group, when the working W pathis established during set-up of the logical conduit 16 between thenetwork elements 14. For instance, the first working W path with ashared mesh class of service will become the first member of the first1:N protection group on a particular channel or timeslot. Anotherworking W path, which wants to share the corresponding shared protectionP link, now becomes the second member of the 1:N protection group.Accordingly, in the protection P path system shown by example in FIG. 4a, the preferred protection information to be transmitted over thesub-network En is the number of the protection group “1” and the numberof the working member “N” contained in the 1:N number pair. For example,in a 10G line, the maximum number of protection groups can be 192,thereby indicating 192 STS1 1:N protection groups. If the protection Plink for example OC3c, OC12, or OC48, then the maximum number of the 1:Nprotection groups per channel would be less It should be noted thatBellcore specifies the maximum number of protection members to be 14.

The shared mesh protection signaling scheme of the present invention canemploy, by way of example only, the overhead 208 APS bytes K1 and K2 forrepresenting the group number “1” and member number “N”. Traditionally,these K bytes are processed relatively quickly, since the networkelements 14 are designed to process the K bytes as fast as possible forSONET protection purposes at the line level 17 independently of thecontrol layer 15, i.e. interrupt driven. In the present protectionsignaling scheme shown in FIGS. 4 a, b, c, it is desirable that thegroup “1” and member “N” information, transferred between the networkelements 14 by way of the protection signals 38, does not exceed thecapacity of the K1 and K2 byte content, wherein for a 10G line themaximum number of protection groups would be 192 and the Bellcorestandard for the maximum number of protection members is 14. Thesevalues can be represented by the K1 and K2 bytes, where use of the K2byte is restricted because of the AIS indication within the K2 byte. Anexample allocation for the protection signaling scheme using the K1/K2bytes is given below, providing an indication of available bit valueswithin the K1/K2 bytes.

K2 bits 1-5 (6-8 limited Ki bits 1-8 use only) Assignment 1111 1111 11111--- Not Used 1111 1111 1111 1101 Reserved for future use (32,761combinations) through through 0000 1000 0000 0100 0111 xxxx xxyy y---Switch Request; x indicates the protection group number (6 bits); yindicates the protection group member (3 bits) 0110 xxxx xxyy y---Acknowledgement of Switch Request; x indicates the protection groupnumber (6 bits); y indicates the protection group member (3 bits) 0101xxxx xxyy y--- Negative Acknowledgement of Switch Request; x indicatesthe protection group number (6 bits); y indicates the protection groupmember (3 bits) 0100 xxxx xxyy y--- Revert back to working request; xindicates the protection group number (6 bits); y indicates theprotection group member (3 bits) 0011 xxxx xxyy y--- Acknowledgement ofRevert back to working request, x indicates the protection group number(6 bits); y indicates the protection group member (3 bits) 0010 00001111 1--- Lockout of protection 0010 0000 1111 0--- Forced Switch 00100000 1110 1--- Reserved for SF - High Priority 0010 0000 1110 0---Reserved for SF - Low Priority 0010 0000 1101 1--- Reserved for SD -High Priority 0010 0000 1101 0--- Reserved for SD - Low Priority 00100000 1100 1--- Manual Switch 0010 0000 1100 0--- Wait-to-Restore 00100000 1011 1--- Reserved for Exercise 0010 0000 1011 0--- Reserved forfuture use (1045 combinations) through through 0000 0000 0000 1--- -------- ---- -111 AIS-L ---- ---- ---- -110 RDI-L 0000 0000 0000 0--- NoRequest (Idle)

Accordingly, for the above example K byte values, one 10G fibre contains192 STS1s. Therefore, the absolute maximum value in this example for thegroup number now referred to as “x” can never be greater than 192, i.e.there can not be more than 192 1:N protection groups on one fibre Thisassumes that the 1:N groups are all of an STS1 size. If larger sizes areused, for instance OC3 and larger, the number of possible 1:N groups forfibre is reduced For example, only four OC48 1:N groups are possible onone 10G fibre. The value of the member number N in Bellcore 1:Nstandards is a maximum of 14, which hereafter is represented by “y”Hence the largest value for the (x,y) group, member pair can be “192,14” requiring 8 bits for “192” representation with “14” requiring 4 bitsfor representation. The largest value that can be supported by the K1and K2 bytes is: 8 bits of the K1 byte and 5 bits of the K2 byte. Bits 6to 8 of the K2 byte are used for AIS-L and RDI-L signaling, thereforetotaling 13 available bits. One available bit can also be used toindicate whether the K1/K2 bytes are sending a protection switch requestverses a link failure indication through the protection signals 38 (seeFIG. 5) The K byte message (x, y) can also use 1 bit indicating “linkfailure” and the remaining 12 bits can be used to indicate the linkidentity. Indication of the failure can be inserted into the K1/K2Bytes, such as but not limited to using the AIS-L. Furthermore, a coupleof bits can be used for special messages (ACK, NACK, etc.). Therefore,reserving 3 bits (4 messages) for this purpose leaves 10 bits forprotection path identification, which if 64 1:N protection group (6bits) with 7 member (3 bits) each per fibre or combinations thereof. Itshould be noted that 2 bits can be kept in reserve which are availablefrom the extended K byte. It is therefore recognized for suitable sizedprotection group and member pairs (x,y) that the K2 byte could representthe group number “y” and the K1 byte the member “y”

Referring to FIG. 4 a, the simplified shared mesh network sub-structureEn is presented for clarity purposes only to help demonstrate the globalprotection scheme of the shared protection class of service. The sharedpath protection set-up of the sub-network En consists of a series ofnetwork elements 14 indicated as 1, 2, 3, 4, 5, 6 with a correspondingnumber of OCC's 28 indicated as OCC 1, OCC 2, OCC 3, OCC 4, OCC 5, andOCC 6. The network elements 14 are interconnected by the conduits 16,logical and/or physical, with solid line connections A-B and C-Ddenoting the working W paths and the dotted line paths 1-3-4-2 and5-3-4-6 between the network elements 14 denoting the potentialprotection P paths. The term “working” refers to the routes andequipment involved in carrying the STS-1 frames 200 on the sub-networkEn during the normal mode of operation, and the term “protection” refersto the routes and equipment involved in carrying the STS-1 frames 200 onthe sub-network En during a failure mode of operation. It is recognizedthat each protection P path is made up of a series of individualprotection links between adjacent network elements 14. For instance,protection P path for the working W connection or path AB includesprotection links 1-3, 3-4, and 4-2. It is further recognized that theprotection link 3-4 is shared between working connections AB and CD. Itis further recognized that each of the working W paths can involve oneor more working links. For instance, working connection AB has theworking W path containing working link 1-2, while the working connectionAB for FIG. 5 contains three working links 1-7, 7-8, and 8-2.

The “normal mode of operation” refers to the operation of thesub-network En when all conduits 16 between the network elements 14 areuninterrupted and the elements 14 operate without faults. The term“failure mode of operation” refers to the operation of the sub-networkEn when some of the conduits 16 between some network elements 14 areinterrupted due to, such as but not limited to a cable cuts or elementfailures It is recognized that the working W and protection P paths cancontain a number of defined working and protection channels or timeslotsrespectively, which are dependent upon the OC-N format and subsequentsetup of the sub-network En when the connections A-B, C-D are defined.

Referring to FIGS. 4 a and 4 b, each controller OCCn of the sub-networkEn has stored a corresponding connection map Mn of all network elements14 used in the working W and protection P paths containing theassociated conduits 16. These connection maps Mn are indicated as M1,M2, M3, M4, M5, M6, which contain connection information for all networkelements 14. Referring to FIG. 4 b, various example connection maps Mnare presented that correspond to the network structure of sub-network Enof FIG. 4 a. For example, map M1 is stored at controller OCC1 andcontains a working connection A-B between elements 1 and 2 (AB-W-12),and a protection P path for the working connection A-B identified ascontaining network elements 1,3,4,2 (AB-P-1342). Accordingly, the otherconnection maps Mn for the remaining maps M2, M3, M4, M5, M6 follow asimilar nomenclature for each map Mn entry. It should be noted theworking connections A-B and C-D are protected via the protection P pathsrepresented by the dotted lines Therefore, between network elements 3and 4 a protection segment 3-4 is shared by the working connections A-Band C-D. When the protection P path of the working connection A-B isset-up, the connection information contained in map M1 is stored at thecontrollers OCC3 and OCC4 in maps M3 and M4, since their correspondingnetwork elements 3, 4 are contained within the protection P path for theworking W path interconnection between network elements 1, 2. Similarly,the protection information of maps M5 and M6 are also present in themaps M3 and M4 Accordingly, the connection maps Mn give the OCCs 28 thecomplete network connection architecture of the path layer 17 for thedefined connections A-B, C-D

During the set-up of the protection P paths for the working connectionsA-B and C-D, nodal diversity is accounted for to reduce the risk ofunprotected working W paths in the event of network failures.Accordingly, at the controllers OCC3 and OCC4, the connection maps M1and M2 for the working connection A-B will be compared by a comparisonfunction with the connection maps M5 and M6 corresponding to the workingconnection C-D. This comparison function helps to provide node diversityof the shared mesh protection signaling scheme. If the comparisonfunction determines that there is no overlap of the working W orprotection P paths contained in the connection maps M1, M2, M5, M6, thenthe working connections A-B and C-D are assigned the shared protection Ppath situated between network elements 3 and 4 On the contrary, ifcomparison function of the connection maps M1, M2, M5, M6 indicates thatthe interconnections between the corresponding network elements 14 arenot diverse, then the protection P path is either assigned to another1:N group of a corresponding port 33 of the network elements 14, or theconnection is not acknowledged (NACK) to the respective source networkelements 1, 3, 6 (see following discussion on FIG. 4 c) for another tryvia a different route mapping. The process of setting up node diversityis to help prevent the situation in which two or more working W paths,sharing a common protection P path, are susceptible to interruption bythe same failure. However, it is noted that the simultaneous failure ofmultiple working W paths could produce the undesirable result of onlyone of the interrupted working W paths being able to use the commonlyassigned protection P path.

Accordingly, in the above described sub-network En, the selection andsubsequent assignment of 1:N protection P paths is now reduced tocomparing a list of network elements 14 by the OCCn in the context of aunique identification for each of the specified protection P paths It isrecognized that alternative arrangements of the example sub-network Enshown in FIG. 4 a can be used to implement the above described sharedprotection P path setup, such as an additional working W path betweennetwork elements 3 and 4 (see FIG. 8).

Referring again to FIG. 4 a, the hardware of the network elements 14have the ports generically identified as 33, which are specificallylabeled respectively as P1, P2, P3, and P4 for each of the networkelements 14 for use in routing identification. The network elements 14also contain, as it is known in the art, switch cards 35 and controlunits 37, such that the switch card 35 of each network element 14 isconnected to the corresponding plurality of ports 33, and the networkelements 14 are configured by the switch cards 35 to couple the ports 33such that STS-1 frames 200 received on one of the ports 33 is output foranother of the ports 33. The control units 37 of the network elements 14are connected to the corresponding switch cards 35, and monitor theadjacent network conduits 16 for a failure 34 (see FIG. 5) affecting theworking W path.

The network elements 14 also have corresponding routing tables R1, R2,R3, R4, R5, R6 (Rn) stored at their respective switch cards 35 withpreloaded data that provides for optimized protection signaling,including a protection P path routing indicator of K byte values (x, y),for example, for insertion into the STS-1 overheads 204, 206. Theserouting tables R1, R2, R3, R4, R5, R6 are defined at the connectionset-up time from data supplied by the OCCs 28 when the working W pathsand corresponding protection P paths are established. It should be notedthat the protection P paths are only implemented in the sub-network Enby the network elements 14 after the working W path fails. Referring toFIG. 4 c, the contents of the routing or protection tables R1, R2, R3,R4, R5, R6 are shown in respect to their corresponding network elements1, 2, 3, 4, 5, 6. Accordingly, each of the network elements 14 havetheir respective local network structure of the overall sharedprotection P path scheme stored in their respective tables Rn associatedwith their switch cards 35

As shown by example in FIGS. 4 a and 4 c, at node A the protection mapR1 has an entry which reads A-B: A-port 2 STS#3 (1,1), which means thatwhen the failure 34 (see FIG. 5) occurs on the connection A-B, theadd/drop port of A is connected to STS#3 of port P2 and the K-byte value1,1 representing the group, member pair is sent to network element 3Upon inspection of protection table R3, the first entry indicates thatwhen the K-byte value 1,1 is received on port P3, then STS#3 on port P3is connected to STS#9 on port P2 and K-byte value 1,1 is sent on port P2towards network element 4. A second entry of the table R3 indicates whenthe K-byte value of 1,2 has been received at port P2, STS#9 on that portP2 must be connected to STS#3 on port P1 and the value 1,1 must be senton port P1 towards node C Accordingly, the entries in the other tablesR2, R4, R5, and R6 can be interpreted similarly. It should be noted inthe sub-network En of FIGS. 4 a and 4 c that the protection channelSTS1#9 is shared on the conduit 16 between network elements 3 and 4(i.e. protection segment 3-4) to protect both working connections A-Band C-D. Accordingly, from the routing tables R1, R2, R3, R4, R5, R6 onecan deduce that working connection A-B is source routed from networkelement 1, while working connection C-D is source routed from networkelement 6. Further, the protection P paths indicated by the dotted linesare built up starting at the source network elements 1, 3, 6 and thecorresponding routing tables R1, R2, R3, R4, R5, R6 are set-up when theworking connections A-B, C-D are initialized by the OCCs 28 of thecontrol layer 15 (see FIG. 2).

Accordingly, when a network failure 34 (see FIG. 5) is detected on theworking P path between network elements 1 and 2, the destination networkelement 2 could send an appropriate failure indication signal 38 (seeFIG. 5) to the corresponding source network element 1 along theavailable protection P paths 2-4-3-1 or 2-1. Similarly, upon detectionof a network failure on the working P path between network elements 5and 6, the destination network element 5 could send the appropriatesignal 38 to the corresponding source network element 6 along theprotection P path 5-3-4-6. It is noted that in a mesh network, thefailure 34 of the working W path is typically detected at the adjacentnetwork element 14 where the affected working channels of the failedworking segment of the working W path are terminated. The requiredprotection switching in the sub-network En is done by the networkelements 14 in the path layer 17 (see FIG. 2), and protection switchingis therefore initiated from the various source network elements 1,6.Further details of the global protection scheme are given below withreference to the example sub-network En given in FIG. 5.

Referring to FIG. 5, an alternative embodiment of sub-network En isshown with interconnected network elements 1, 2, 3, 4, 5, 6, 7, and 8The line failure 34 has occurred between the intermediate networkelements 7 and 8, which is subsequently detected by network elements 7and 8 for cases of bi-directional communication of the data packets 20over the sub-network En (i.e. both network elements 7 and 8 can beconsidered as receiving network elements 14, depending upon thetransmission direction for the defined working and protection channelspresent in the working W and protection P paths) It is noted thatnetwork elements 14 operating in a transmission capacity may not detectthat the failure 34 has occurred in the working W path, for failedworking channels that serve only as transmission conduits 16 for therespective network element 14 Notwithstanding, the network elements 7,8detecting the failure 34 transmit the signal 38 over the path layer 17(see FIG. 2) to the appropriate source/destination network elements 1,2.Accordingly, application of the global protection scheme provides for noprotection switching done at the intermediate network elements 7, 8.Instead, the network elements 7,8 propagate the signal 38 directly overthe path layer 17 to the source and destination network elements 1,2,which coordinate the set-up of the protection switching over theassigned shared protection P path 1-3-4-2 (as given in the connectionmaps Mn). Preferably, the transmission of the signal 38 is not directedover the control layer 15 for subsequent use by the OCCs 28 (see FIG. 2)to become involved in the set-up of the protection P paths. Instead, thefailure detection, notification (signals 38), and resultant protection Ppath set-up (according to tables Rn) are accomplished by the networkelements 14 (over the path layer 17) independently of the OCCs 28.

Referring again to FIG. 5, the control units 37 (see FIG. 4 a) of thenetwork elements 7, 8 monitor for the failure 34 within the workingconnection A-B. Accordingly, once the failure 34 is detected by theSONET layer, the corresponding control units 37 of the affected networkelements 7, 8 further operate to determine protective switching datacorresponding to the failure 34 and to insert the protection switchingcontained in data of the routing tables Rn within the overhead 204, 206of the STS-1 frame 200 of the signal 38, such as but not limited tousing AIS-L for insertion. This data from the routing tables Rn is thentransmitted in the protection signal 38 from the corresponding ports 33(see FIG. 4 a) of the affected network elements 7, 8. Accordingly, tofacilitate the indication of the line failure 34 to the source networkelement 1, the associated conduits 16 (either working W and/orprotection P paths) leading back to the source element 1 are floodedusing the K byte value (x, y) of the signal 38 The source networkelement 1, protecting the working connection A-B, will use the K bytesvalue (x, y) retrieved from in the STS-1 overhead 204, 206 of the signal38 to identify the line failure 34 along the defined protection P pathtowards the destination network element 2 (providing the identity of theworking connection A-B that failed), thereby causing the assignedprotection P path 1-3-4-2 to be set-up through reconfiguration of theswitch cards 35 of the corresponding network elements 1, 3, 4, 2.

Accordingly, a protection switch is triggered at the source networkelement 1 and the appropriate switch selection is done at thedestination network element 2 to resume continuity of potentialtransmissions of data packets 20 originally destined for the failedworking W path 1-7-8-2. It should be noted in the above example that forthe affected network element 7, the K-byte value (x, y) from thecorresponding routing table R7 is inserted into the overhead 204, 206K1/K2 bytes of the signal 38, which is eventually received by the sourcenetwork element 1 and thereby reports the identified failure 34. In thiscase, the failure indication in the signal 38 is transmitted back to thesource network element 1 in the conduits 16 (see FIG. 4 a) that areincluded in the failed working W path of the connection A-B.

It should be noted a consequence of assigning the protection P path1-3-4-2 by the global protection scheme (to replace the failed working Wpath 1-7-8-2) is that all available protection channels present in theprotection P path 1-3-4-2 are no longer available to protect anysubsequent potential failures occurring on the working connection C-D.This is a result of the shared protection segment 3-4 of the protectionP path being assigned to both the connections A-B and C-D. However, theprocess of nodal diversity helps to reduce the occurrence ofsimultaneous failures occurring on both the working connections A-B andC-D. The implementation of the global protection signaling scheme in themesh sub-network En can provide advantages similar to ring or pathswitching in ring networks.

Accordingly, using the above-described global routed mesh protectionscheme, suitable information can be exchanged in the K1 and K2 bytes touniquely identify the set-up of the protection P paths for correspondingworking W paths in a one to many sub-network En configuration. It isrecognized that other suitable overhead bytes of the overhead 204, 206could be used in place of the K1/K2 bytes, given above by way of exampleonly. It should be noted that the elapsed time, from failure detectionby the SONET layer to the eventual configuration of the switch cards 35in the selected protection P path, is preferably less than 200 msecbased on the noted example sub-network En of 200 network elements 14.

In the present shared mesh protection signaling scheme controlled by thesource network elements 1,3,6, the exchange of K-byte values (x, y) bytwo network elements 7, 8 (see FIG. 5) may have no absolute confirmationguarantee that the respective K-byte (x, y) has been read by theadjacent corresponding network elements 1, 2 before the next value (x,y) is sent. Therefore, it is assumed that the transmitted K-byte values(x, y) will be read in time for adequate protection switch processing.Therefore, for those K-byte values (x, y) that are not read in time, are-send operation can be done in the event that the correspondingnetwork element 14 does not receive an ACK or NACK. However, it isrecognized that the re-send operation may be performed with an inherentdelay hence there may be no guarantee that the result of the re-sendwill still be within the desirable switching protection limit of lessthan 200 msec. In operation of the described K-byte value (x, y)exchange, as further described below, the corresponding network elements7, 8 sending the K-bytes (x, y) will send the same value (x, y) for apre-determined number of msec. It can then take the correspondingnetwork element 14 up to 0.375 msec, 3 frames for example, to validatethe K-byte values (x, y) and generate an interrupt signal. The interruptsignal will cause the network element 14 to read the K-byte value (x, y)and put it on a cue for processing. The pre-defined validation timeperiod will be set such that under heavy load conditions at thereceiving network elements 1, 2 the number of lost K-byte values (x, y)is less than 99.999%, or any other suitably acceptable tolerance for aparticular architecture of the sub-network En.

In the event that a K-byte value (x, y) does not get read in time and isoverwritten in the STS-1 overhead 204, 206, care should be taken toprovide that the overwritten K-byte value (x, y) is re-transmitted.However, when certain K-byte values (x, y) are lost then either theprotection switch request message or the ACK/NACK could also be lost.Therefore, a possible result of either of these two cases is that thesource network elements 1,6 will not receive the ACK or the NACK.Accordingly, after sending the K-byte message request (x, y), therouting source network elements 1, 6 can start a timer, whereby afterthe timer expires corresponding protection request can be put asideuntil all other protection switches of the corresponding protection Ppath(s) have been completed. At this time, the corresponding networkelements 1, 6 can re-try the previously failed protection switch.Further implementation is that after for example three failed attemptsthe source network elements 1, 6 can give up the message requests andraise an alarm condition indicating the failure of the intended messagerequest. It is recognized that a consequence of the failed protectionswitch request can be that a part of the protection P path(s) has beenset-up from the termination network element 2 towards the routing sourcenetwork element 1. Accordingly, since the complete protection P path isreserved for the protection switch, no misconnection can result.Therefore, if the network elements 14 can not set-up the desiredprotection P path, the source network element 1 will keep trying torelease the protection P path to ensure there is no unclaimed protectionP path connection(s) in existence.

Referring to FIG. 6, the operation of the global shared protectionsignaling scheme can be performed automatically through the use ofsoftware and/or associated hardware as will be described herein below.At step 100, the required level of protection for each conduit 16 isdetermined by the management system 22, in response to connectionrequirements 24 received and/or anticipated from the clients 26. Next,the network 10 and sub-networks An, Bn Cn, Dn, En architecture, asdepicted by example in FIGS. 1 and 2, are selected 102 from availablenetwork resources for network elements 14 and conduits 16, to be usedfor both the protection P and working W paths to satisfy the customerrequirements 24 It is recognized that preferably the shortest paths arechosen as the working W paths and the next most optimal paths are chosenas the corresponding protection P paths in a 1:N relationship, subjectto other considerations such as load capacity, nodal diversity, andcost.

At step 104, each controller OCCn 28 of the sub-network En stores acorresponding map Mn of all network elements 1, 2, 3, 4, 5, 6 used inthe path of each conduit 16. These connection maps Mn identify theparticular working W paths and the network elements 14 they contain, aswell as the related protection P paths and their contained networkelements 14. In diverse environments, the connection maps Mncorresponding to adjacent working W paths are compared 106 so as tocheck whether there is no overlap of working W or protection P pathscontained in the maps Mn. The degree of acceptable overlap will beaccording to a predefined tolerance. Accordingly, in the event nooverlap is confirmed, the specified working W paths can share thedefined protection P path selected (i.e. 1:N protection scheme). On thecontrary, if the interconnections between the network elements 14 6 arenot diverse, then the protection P paths can be redefined untildiversity is achieved.

Next, the routing table Rn information is defined 108 and stored at thenetwork elements 14 with the routing table Rn data (see FIG. 4 c) thatwill be used in the event of protection path P initialization. Theprotection switching data of the table Rn includes the switching datathat is inserted within the K1/K2 protection bytes of the overhead 204,206 of the STS-1 frames 200 once a particular failure mode 34 occurs.These K-byte values (x, y) are transmitted in the opposite direction ofwhere the failure 34 occurred by the network elements 14 detecting thefailure 14, for eventual reception by the source network elements. 14The routing table Rn data defines conduit 16 modifications that arerequired to be performed within the switch cards 35 of the networkelements 14 included within the protection P paths, to implement there-routing of failure affected transmission of the data packets 20represented by the STS-1 frames 200. The K byte values (x, y) aredefined 110 in the routing tables Rn for use in the event the failuremode 34 is detected. Accordingly, the K1 byte is used to define thegroup number “x” and the K2 byte is used to define the protection groupmember “y”. The function of the K byte value (x, y) is to direct thecorresponding network elements 14 making up the protection P paths tocross connect the required ports 33 and time slot information (see FIG.4 c), thus resulting in protection P path generation once the failure 34has been detected.

Next, the switch cards 35 of the network elements 14 concerned with thevarious defined working W paths are configured 112 to dictate whereparticular customer STS-1 frames 200 will be routed during normaloperation of the sub-network En. The combined effect of the switch card35 configurations is the defining of the optical carrier conduits 16 andthe network elements 14 that are to be used if STS-1 frame 200 isreceived during the working or normal mode of operation of thesub-network En, on a particular port 33 within a path terminationsub-network element En. After definition and set-up of the working Wpaths, the network 10 operates in normal mode 114 until the failure 34is detected, as detailed below. However, in the event the working W orprotection P paths are modified prior to failure mode 34 in thesub-network En, then the maps Mn and tables Rn are updated 116 asrequired.

Referring to FIG. 7, the failure mode operation of the sub-network En isdescribed for the global shared protection signaling scheme. From thenormal mode of operation at step 114 of FIG. 6, the failure 34 isdetected in the path layer 17 of the sub-network En at step 118 by thenetwork elements 14 adjacent to the failure 34. These adjacent networkelements 14 look-up the protection entries within their correspondingrouting tables Rn at step 120 and insert 122 the protection switchingdata of their entries into the corresponding K1/K2 byte values (x, y) ofthe STS-1 frames 200 of the signals 38. Accordingly, the signals 38 withassociated values (x, y) are directed 124 to the source network element14, and then over the protection P path to the destination networkelement 14 to provide for setup of the protection P path. If the ACK isreceived by the source network element 14 from the destination networkelement 14 at step 126, then the defined protection P path contained inthe tables Rn is established at step 128 by appropriate switch card 35reconfiguration. Therefore, the STS-1 frames 200 of the data packets 20originally destined for transmission on the original failed working Wpath are redirected 130 along the established protection P pathcontaining the inserted protection bytes K1, K2 until the originalworking W path is re-established 132, 134 through failure correction.However, in the event that the failure 34 is not corrected within apre-determined time interval, the protection P path can become the newworking W path at step 136 and accordingly alternative protection Ppaths can be established by updating the maps Mn and tables Rn by theOCCs 28 at step 138 accordingly. Subsequently, the sub-network En canreturn to normal operation mode at step 114, which can be accomplishedthrough use of the K1/K2 bytes to reestablish the original working Wpath in much the same way that the now outdated protection P path wasestablished.

Conversely, if the ACK is not received at step 126 when the set-up ofthe protection P path is attempted, then the K bytes K1, K2 are resentuntil a timeout occurs 140 or the ACK is finally received, whichever isfirst. If the timeout at 140 is received, then the corresponding sourcenetwork element 14 signals an alarm at 142 over the sub-network En tothe OCCs in the control layer 15 that the defined protection P pathcannot be established. It is further recognized that an alternate 2^(nd)choice (3^(rd) etc.) of the protection P paths could be contained withinthe tables Rn as part of the timeout procedure described above (i.e. asan alternative to the alarm signal transmission).

Accordingly, the content of the K byte message is in the form of (x,y).When the 1:N protection P paths are added to the sub-network En, theprotection bandwidth should be reserved and a number can then beallocated to each 1:N group by the K bytes on each corresponding port 33located between two adjacent network elements 14. Therefore, the K bytemessage format used in the present protection scheme can be (x,y) wherex is the protection group number on the corresponding port 33 and y isthe protection group member. It should be noted for each generic port 33there is a protection routing table Rn for the 1:N traffic potentiallycarried on that port 33. This measure can reduce the number of look-upsrequired, since only the protection routing table Rn for a particularport 33 is searched for the appropriate entry. Furthermore, the add/dropports are indicated by references A, B, C, and D for simplicity inregard to the connections A-B and C-D In addition, the switch cards 35of the network elements 1, 2, 3, 4, 5, 6 are set-up from the sourcenetwork elements 1, 3, 6. It is noted that detailed design of particularprotection routing data in the routing tables Rn is dependent upon theparticular messaging scheme selected and implemented. Furthermore, theuse of K1 and K2 bytes for providing desired switching times preferablyless than 200 msec is done by way of example only, wherein othersuitable overhead bytes in the transport overhead 204 and path overhead206 could also be used, if desired. Preferably, the overhead bytesselected should be interrupt driven, as to help optimize the resultantswitching times. It is further recognized that the preferably less than200 msec overall protection switching time is with reference to anexample 200 network element 14 sub-network En with 3000 km of conduct 16in both the working W and protection P paths. Accordingly, otherdesirable switching times can be more or less than the 200 msecreference given, based on the corresponding size of the sub-network En.

The shared mesh protection signaling scheme provides a 1:N protection,i.e. one protection path provides protection facilities for N workingpaths. Accordingly, the shared protection path scheme can provide formultiple diversely routed working connections A-B, C-D sharing a commonprotection path 3-4, (see FIG. 4 a). This protection path can be an STS1or any of the SONET/SDH combinations such as OC 12/48, as long as thesub-network En infrastructure supports these combinations. Further, onefibre of the conduit 16 can accommodate Dedicated Mesh (l+1), SharedMesh (working and protection from different 1:N protection groups), MeshReroute, Unprotected and Pre-emptable, all on the same fibre. This canhelp to provide optimised usage of available sub-network En bandwidth.

The shared mesh protection signaling system can provide sharing of thedata used during call set-up and data used for restoration once afailure is detected. Accordingly, connection data can be kept by theOCCs 28 in the control layer 17 to provide 1:N connections, so as tohelp facilitate the set-up of diverse routes for all working W andprotection paths P in the 1:N group for signaling between the OCCs 28.It is considered that the call set-up is not time critical in regard tofast protection switching. Furthermore, the restoration or routing datacan be stored at the network elements 14 to provide 1:N protectionswitching The routing data can be kept at the switch cards of thecorresponding network elements 14 to provide signaling in the path layer17 between corresponding network elements 14, with the signaling doneusing the STS-1 overhead 204, 206. It is noted that typically therespective hardware of network elements 14, such as the switch cards 35,have interrupt driven priority access to some of the overhead bytes,such as but not limited to the K1/K2 byte values, and can thereforedynamically act on the protection signaling information containedtherein independently of OCC 28 involvement. It is considered thatminimizing restoration time is critical in protection signaling systems.

A further embodiment of the sub-network En, shown in FIG. 8, is nowreferenced to describe the local shared protection signaling scheme. Thesub-network En has eight network elements 14 in the path layer 17, asindicated by reference numerals 1,2,3,4,5,6,7, and 8 respectively. Anexample representation of the control layer 15 contains thecorresponding series of OCCs 28 coupled together by links 32, whereineach OCC 28 corresponding to each network element 14 is indicated byOCC1 to OCC8 respectively. The OCCs 28 communicate with the individualnetwork elements 14 though the series of links represented genericallyby reference numeral 31. The routing tables R1,R2,R3,R4,R5,R6,R7, and R8are similar in data content and function to those discussed inconnection with FIGS. 4 a,b,c, whereby working connection A-B is sourcerouted by network element 1, working connection C-D is source routed bynetwork element 6, and working connection E-F is source routed bynetwork element 3. Therefore, network elements 2, 4, and 5 can beregarded as destination elements for their respective connections A-B,E-F, and C-D. It is noted that the working W paths can contain one ormore working links, while the shared protection segments of thesub-network En can include at least one protection link. Protection Ppaths can comprise one or more of the shared protection links.

The path layer 17 of the sub-network En contains, for example, the threeworking W paths represented by solid line paths, namely workingconnection A-B with network elements 1,7,8,2, working connection C-Dwith network elements 5,6, and working connection E-F with networkelements 3,4. Further, when the sub-network En was established, theworking connection A-B was assigned a protection P path indicated by thedotted line path 1-3-4-2 consisting of protection segments 1-3, 3-4, and4-2, the working connection C-D was assigned a protection P pathindicated by the dotted line path 5-3-4-6 consisting of protectionsegments 5-3, 3-4, and 4-6, and the working connection E-F was assigneda protection P path indicated by the dotted line path 3-1-7-8-2-4consisting of protection segments 3-1, 1-7, 7-8, 8-2, and 2-4.Accordingly, the working connections A-B and C-D share the protectionsegment 3-4 situated between the network elements 3 and 4. It isrecognized the number of working and protection channels on each workingconnection A-B, C-D, E-F and corresponding protection P paths aredependent upon the particular OC-N format and capabilities used by thesub-network En. It should be noted that protection segment 7-8 isseparate from the assigned protection P path 1-3-4-2 for the workingconnection A-B.

Referring to FIG. 9, a line failure 40 has occurred on the workingsegment 7-8. Therefore, all channels configured on the working segment7-8 are no longer available for transmission of the data packets 20 (seeFIG. 2) between the source network element 1 and destination networkelement 2. It should be noted that, for exemplary purposes only, workingconnection A-B is further denoted in FIG. 9 as having assigned workingchannels STS#1, STS#2, and STS#3 for transmission of the data packets 20between the source network element 1 and destination network element 2.The protection P path 3-1-7-8-2-4, including protection segment 7-8, andprotection P path 1-3-4-2 have also been further subdivided to haveavailable protection channels STS#15 to STS#20 inclusive, for exemplarypurposes only.

However, contrary to the global routed protection signalling schemediscussed above with reference to FIG. 5, the alternate locally routedprotection signalling scheme is now described. Referring to FIGS. 9 and10, the failure 40 is first detected at step 300 by the SONET layer ofthe adjacent network element 8, as for example the network element 8 isthe node at which the working channels STS#1-3 are destined. The controlunit 37 (see FIG. 4 a) of the network element 8, under the globalprotection scheme, would further operate to determine appropriateprotective routing table Rn data corresponding to the detected failure34. However, under the local protection scheme, before inserting theprotection switching contained in data of the routing table R8 withinthe overhead 204, 206 (see FIGS. 3 a and 3 b) of the STS-1 frame 200, anidentification module 18 of network element 8 checks locally 302 to seeif there are any available local protection channels between itself andthe network element 7 located on the opposite side of the failure 40.The identification modules. In contain a listing of potential protectionchannels present between adjacent network elements 14. If adequate localprotection channels are available (i.e. in this case any of the channelsSTS#10-15 on protection segment 7-8), then the network element 8 willattempt to initiate a local protection switch 42 at step 304. This localprotection switch can be defined as protection switching (done by thelocal source network element 7) and subsequent switch selection (done bythe local destination network element 8) upon confirmation of theintended local switch by the affected network elements 7,8 on eitherside of the failure 40. It should be noted that the other networkelements 14 have corresponding identification modules I1, I2, I3, I4,I5, I6, and I7 (In) respectively.

Accordingly, after the failure 40 has been detected by the networkelement 8, network element 8 becomes the switching node according tostandard SONET switching protocols. The network element 8 then insertsthe appropriate K1 and K2 byte indications into the SONET line overhead204, 206, for transmission on any of the potentially availableprotection channels STS#10-15 of the protection segment 7-8, totransport the required protection switch request 44 to the networkelement 7. A scheme selection function of the identification module I8confirms that the local protection channels STS#10-15 are available onthe local protection segment 7-8. After confirmation, the schemeselection function selects the local protection switching scheme overthe global scheme and the network element 7 executes the localprotection switch 42 by the switch card 35 to redirect any incoming datapackets 20 away from the failed working path channels STS#1-3 on workingsegment 7-8, and sends an ACK of the switch request received fromnetwork element 8, along with an indication of the protection channelsselected from those available A channel selection function of theidentification module I7 selects a portion STS#13-15 of the availableprotection channels STS#10-15 to help maximize local network bandwidthefficiency. Network element 7 is now setup to cross connect all incomingdata packets 20, originally destined out from network element 7 on theworking channels STS#1-3 of working segment 7-8, onto the selectedprotection channels STS#15-18 of protection segment 7-8 destined tonetwork element 8.

It is recognized that the network element 8, after receiving the ACKfrom the network element 7 and confirmation of the selected protectionchannels (STS#15-18), will choose to receive the data packets 20 by aswitch selection 46. The network element 8 also configures 308 theswitch selection 46 by it's switch card 35 to direct any potential datapackets 20 from the protection channels STS#15-18 of protection segment7-8 back to the original working channels STS#1-3 on the working segment8-2 of the working connection A-B. Accordingly, neither the sourcenetwork element 1 nor the destination network element 2 were directlyinvolved in the local switches 42, 46, and therefore continue totransmit and receive the data packets to the original working segment1-7 and from the original working segment 8-2, respectively, of theinitially established working connection A-B. Further, it is recognizedthat switching 42 and switch selection 46 of working channels STS#1-3onto protection channels STS#15-18 is irrespective as to whether thenetwork traffic is present on the working connection A-B.

Therefore, as a result of the detected failure 40, the modified workingW-protection P path for the original working connection A-B now consistsof the original network elements 1, 7, 8, and 2, except the segments nowutilized are the working segment 1-7, a portion of the protectionsegment 7-8, and the working segment 8-2 The modified working connectionA-B now contains a locally protected segment (i.e. protection segment7-8) and the entire protection P paths 1-3-4-2 and 5-3-4-6 remainavailable for the recovery of other potential failures, such as on theworking connection C-D. It is noted that this local or segment switchingfor mesh networks could be 1:N or M:N and can provide advantages similarto span switching in ring networks. This is compared to the previouslydescribed global protection signaling scheme which can provideadvantages in mesh networks similar to the ring/path switching in ringnetworks.

The network elements 7,8 continue to monitor 312 for correction of thefailure 40. Once the line failure 40 is corrected, the network elements7,8 execute a reverse procedure to that described above in order torelease 314 the assigned protection channels STS#15-18 of the protectionsegment 7-8 and remove the protection switch 42 and switch selection 46.This places the protection channels STS#15-18 of protection segment 7-8back on to the original working channels STS#1-3 of the working segment7-8 utilizing appropriate SONET switching protocols (such as firstremoving the destination end switch selection 46 following a wait torestore period), and then the transmission of the data packets 20resumes 316 along the working connection A-B as per the pattern shown inFIG. 8. It is recognised that working channels other than the originalSTS#1-3 configuration could be utilized on the working W path 1-7-8-2,if desired, once the line failure 40 has been corrected.

However, if no local protection channel is available at step 302 betweenthe two network elements 7,8, as confirmed by the scheme selectionfunction of the identification module 18, then the protection signal 38(see FIG. 5) containing the failure indication with an appropriate Kbyte value (x,y) is propagated at step 120 (of FIG. 7) to the sourcenetwork element 1, as per the above described global protectionsignalling scheme with reference to FIGS. 5, 6, and 7. Accordingly, whenthe network elements 7,8 confirm that no local protection channels areavailable at step 302 of FIG. 10, step 120 and subsequent steps of FIG.7 (indicated by connector “A”) are followed by the affected networkelements 14 to implement the global protection signalling scheme.

It should be noted that the above-described local protection switchingscheme uses only a portion of the locally available protection channels,if permitted, as compared to all available protection channels. Thisability of the channel selection function of the identification modulesIn helps to support asymmetrical working versus protection capacity forincreasing bandwidth efficiency on the sub-network En, as well as makeunused protection bandwidth available to provide protection forsubsequent failures occurring on the other working connections C-D, E-F.It is also recognized that the usage of the portion of protectionchannels STS#15-18 could be reported by the network elements 7,8 to theOCCs 28 and/or the affected network elements 14 of the adjacent workingconnections C-D and E-F, which may require usage of some or all of theassigned protection P path 1-7-8-2, if shared. Accordingly, the routingtables Rn and identification modules In could be updated subsequently tothe set-up of the local protection switch 42 and switch selection 46 toreflect usage of the local protection channels STS#15-18 on theprotection segment 7-8 It is also recognized that the routing tables Rnand identification modules In could be combined as one table/module.

Further, it is recognized that the local protection switching schemedoes not have to use the group and member numbers in the K1/K2 bytes, asdone in the global scheme. Rather, the interrupt driven bytes are usedby the local scheme to determine if bandwidth is available for localprotection switching.

In regard to the quality of path sizes in diverse routing applicationsfor both the local and global protection signaling schemes, it is alsopossible to mix different sizes of the 1:N protection groups. Forinstance, a smaller one will fit in a larger one (many STS-1s into oneOC48c). However, concatenated payloads can start at certain STS-1boundaries, such as OC12c starts at STS-1, STS-13, etc. Accordingly,mixing of 1:N groups can also feature to optimize protection bandwidthby analysing on a segment-by-segment basis which protection groups canshare protection bandwidth, through updating of the routing tables Rnstored at the network elements 14.

It should be noted that one working W path can have many protectiongroups, each with many members For example link “1” between two networkelements 14 can have three protection groups, with each five members.Link “2” between these two same network elements 14 can have another 2protection groups with each 3 members, while link 3 between these samenetwork elements 14 may not have any 1:N protection groups. Thecorresponding OCC 28 needs to keep track of the 1:N protection groupsassigned at each link and the number of members in the protectiongroups. The OCC 28 must help to ensure that in a 1:N protection groupthere are never more than N members in the protection group.Furthermore, the value of N is defaulted for each working W path and canbe changed through the suitable user interface 23 coupled to theintegrated management system 22 The value of N is only valid for aparticular link. For instance, N could be fixed to its default value orN can be changed, but only on a trunk (bundle of links between twonodes) basis.

It is recognized that conduits 16 having the same source and destinationnetwork elements 14 (for instance 1 and 2 in FIG. 5) can make use of amore optimized global protection signaling scheme. For instance, ifthere are 23 STS1 1:N conduits 16 sourced at network element 1 andterminated at network element 2, and all are protected by networkelements 1-3-4-2 (using 23 STS-1's), only 1 K-byte message (x, y)transmitted from the source network element 1 to network element 3 cansuffice to indicate that all 23 STS-1 need be protection switched. Thiscould require addition information at the corresponding network elements14 to map the one message to the 2-3 connection requests.

Due to the provision of shared protection P paths in both the local andglobal protection switching schemes, it is feasible that collisions foraccess to those paths P can occur. Referring to FIGS. 4 a and c, one wayto help misconnections and collisions is to send the protection switchrequest from the source network element 1 to the correspondingdestination network element 2 to reserve the protection bandwidth, whilethe actual switch actions are done when receiving an acknowledgement(ACK) from the destination network element 2 and working its way back tothe source network element 1. The acknowledgement should be associatedwith the protection switch request and should use the correspondingrouting tables Rn as well as send the correct K byte (x,y) values of theprotection signals 38 backwards. Accordingly, the routing tables Rnshould also be reserved for a reverse lookup. For instance, with thefailure 34 between the working connection A-B in FIG. 4 a, networkelement 2 will send the acknowledgement (1,1) back to network element 4Network element 4, then using its corresponding routing table R4 findsthat this acknowledgement needs to be sent onto port P1 with a value of1,1. It should be noted that this can be deduced by reading the firstentry in the protection table R4 at network element 4 in the reverseorder.

In reference to FIG. 5 in regard to collision behaviour, after thesegment failure 34 has been detected, the source elements 1, 3, 6 willstart routing K1 and K2 bytes to allocated protection P paths. The raceto get access to the 1:N protection P paths can be consideredunpredictable. For example, if both the working W paths A-B and C-D failin a double failure mode, network element 1 will start the race forproviding the protection P path to protect working connection A-B andnetwork element 6 will do the same for working connection C-D. Somewherebetween the network elements 3 and 4 a collision can be expected.Therefore, either the working connection A-B gets the protection P pathbetween network elements 3-4 or working connection C-D is awarded thecorresponding protection P path. Therefore, one of the protection P pathnetwork elements 3, 4 needs to back off with a Not Acknowledgement(NACK) sent back to the corresponding source network element 1, 6.

Furthermore, the above described collision circumstance also providesinsight into a misconnection scenario. Accordingly, when network element1 and network element 3 set-up the protection path to protect workingconnection A-B, and network element 6 and network element 4 do the samefor working connection C-D, the collision can happen between networkelements 3 and 4, and network element 1 will then be temporarilyconnected to network element 3 until the collision gets resolved.Therefore, a forward reservation of the protection path can be providedfor through forward reservation and activation of the switch request onreceiving the acknowledgement sent in the reverse direction This canhave an impact on the switching times.

It is further recognized that above described local and globalprotection switching schemes can be applied on other optical networkformats, such as Optical Transport Networks (OTN) based on DenseWavelength Division Multiplexing (DWDM). DWDM is an enabling technologythat can provide connections between service layer elements of theoptical network at higher speeds on the existing fiber plant, and thusprovide the next step in the evolution of the transport infrastructure.A DWDM-based OTN can provide high capacity per fiber, as well as highcapacity per connection. Each DWDM wavelength provides a connection thatcan carry a number of protocols with a bit-rate ranging from 50 Mb/s to2.5 Gb/s and beyond. These wavelengths can be multiplexed with otherwavelengths and added, dropped and cross-connected at the optical level,helping to eliminate the need to manage the bandwidth at a lowergranularity when it is not necessary. In OTN, a wavelength is notconstrained by a fixed-rate timeslot in a pre-defined multiplexprotocol, and it can carry a number of protocols, such as SONET, ESCON,FDDI, and Ethernet, and any bit-rate, such as 150 Mbs, 1.25 Gb/s and 2.5Gb/s. The flexibility of the DWDM-based OTN derives from the protocoland bit-rate independence of the traffic-carrying wavelengths Protocoland bit-rate independence is a key advantage of DWDM that enablesoptical transport networks to carry many different types of traffic overan optical channel regardless of the protocol (Gigabit Ethernet, ATM,SONET, asynchronous FOTS, etc.) or bit-rate (150 Mb/s, 1.25 Gb/s, 2.5Gb/s, etc.). Accordingly, the interrupt driven overhead bytes of the OTNcan also be used to implement the above described local and globalprotection switching systems.

Although the invention has been described with reference to certainspecific embodiments, various modifications thereof will be apparent tothose skilled in the art without departing from the spirit and scope ofthe invention as outlined in the claims appended hereto.

1. In a mesh network, a network element for providing protectionswitching in a 1:N shared mesh protection scheme having a firstprotection path associated with a pair of working paths selected fromthe N working paths, the network element comprising: a) a link forconnecting the network element to a first working path of the pair ofworking paths in a path layer of the network, the path layer including aplurality of interconnected network elements; b) a routing tableaccessible by the network element, the routing table for having localprotection channel information associated with a local protectionsegment separate from the first protection path, the local protectionsegment connecting the network element and one of the interconnectednetwork elements adjacent to the network element; and c) anidentification module for using the local protection channel informationto identify an available protection channel on the local protectionsegment in the event of failure of a local working segment of the firstworking path, the local working segment connecting the network elementand said one of the adjacent interconnected network elements; whereinthe available local protection channel on the local protection segmentis used to switch local network bandwidth from the failed local workingsegment to the local protection segment after the network failure hasbeen detected; and wherein the protection channel information includes alisting of a plurality of local protection channels associated with thelocal protection segment; said network element further comprising achannel selection function of the identification module to select aportion of the available protection channels from the list, the portionselected to match the bandwidth requirements of the failed local workingsegment.
 2. The network element according to claim 1, wherein a secondprotection path is associated with the N working paths to provide a M:Nshared mesh protection scheme.
 3. In a mesh network, a network elementfor providing protection switching in a 1 :N shared mesh protectionscheme having a first protection path associated with a pair of workingpaths selected from the N working paths, the network element comprising:d) a link for connecting the network element to a first working path ofthe pair of working paths in a path layer of the network, the path layerincluding a plurality of interconnected network elements; e) a routingtable accessible by the network element, the routing table for havinglocal protection channel information associated with a local protectionsegment separate from the first protection path, the local protectionsegment connecting the network element and one of the interconnectednetwork elements adjacent to the network element; and f) anidentification module for using the local protection channel informationto identify an available protection channel on the local protectionsegment in the event of failure of a local working segment of the firstworking path, the local working segment connecting the network elementand said one of the adjacent interconnected network elements; whereinthe available local protection channel on the local protection segmentis used to switch local network bandwidth from the failed local workingsegment to the local protection segment after the network failure hasbeen detected; and further comprising a scheme selection function of theidentification module to select the first protection path afterconfirming the local protection segment is not available for switchingthe local network bandwidth.
 4. The network element according to claim 3wherein the routing table includes protection routing informationassociated with the first protection path and the N working paths. 5.The network element according to claim 4 further comprising a firstidentifier assignable to the first protection path and a secondidentifier assignable to each of the N working paths, the identifiersassociated with the protection routing information.
 6. The networkelement according to claim 5 further comprising a failure value forproviding to at least one of the interconnected network elementsadjacent to the network element the first identifier and the secondidentifier relatable to the failure.
 7. The network element according toclaim 6, wherein the failure value is adapted for insertion into aninterrupt driven overhead byte of a protection signal for transmissionover the mesh network for communication between the interconnectednetwork elements and the network element.
 8. The network elementaccording to claim 7, wherein the failure value is adapted forcommunication in the overhead byte of the protection signal to helpestablish the first protection path after the failure has been detectedin the local working segment of the first working path.
 9. The networkelement according to claim 8, wherein the failure value is adapted foruse in the protection signal selected from the group comprising: aswitch request, an acknowledgement of a switch request, a negativeacknowledgement of a switch request, a revert back to working request,and an acknowledgement of a revert back to working request.
 10. Thenetwork element according to claim 5, wherein the first identifier is afirst byte of a pair of overhead bytes and the second identifier is asecond byte of the pair of overhead bytes.
 11. The network elementaccording to claim 10, wherein the first byte is selected from one of aK1-K2 byte pair and the second byte is selected from the other one ofthe K1-K2 byte pair.
 12. The network element according to claim 4,wherein the protection routing information contained in the routingtable is defined when the N working paths of the path layer areestablished.
 13. The network element according to claim 12, wherein theprotection routing information contained in the routing table issupplied by a controller associated with the network element.
 14. Thenetwork element according to claim 12, wherein the protection routinginformation is distributed in the path layer of the mesh network.
 15. Ina mesh network, a method for providing protection switching in a 1:Nshared mesh protection scheme having a first protection path associatedwith a pair of working paths selected from the N working paths, themethod comprising the steps of: a) interconnecting a network element toa first working path of the pair of working paths in a path layer of thenetwork, the path layer including a plurality of interconnected networkelements; b) defining a routing table accessible by the network element,the routing table having local protection channel information associatedwith a local protection segment separate from the first protection path,the local protection segment connecting the network element and one ofthe interconnected network elements adjacent to the network element; c)identifying by the network element a failure of a local working segmentof the first working path, the local working segment connecting thenetwork element and said one of the adjacent interconnected networkelements; d) using the local protection channel information by thenetwork element to identify an available protection channel on the localprotection segment; e) switching local network bandwidth from the failedlocal working segment to the available protection channel on the localprotection segment; f) storing in the protection channel information alisting of a plurality of local protection channels associated with thelocal protection segment; and g) selecting a portion of the plurality oflocal protection channels from the listing.
 16. The method according toclaim 15, wherein the portion is selected to match the bandwidthrequirements of the failed local working segment.
 17. The methodaccording to claim 15 further comprising the step of selecting the firstprotection path after confirming the local protection segment is notavailable for switching the local network bandwidth.
 18. The methodaccording to claim 17 further comprising the step of storing in therouting table a protection routing information associated with the firstprotection path and the N working paths.
 19. The method according toclaim 18 further comprising the step of assigning a first identifier tothe first protection path and assigning a second identifier to each ofthe N working paths, the identifiers associated with the protectionrouting information.
 20. The method according to claim 19 furthercomprising the step of propagating a failure value to at least one ofthe interconnected network elements adjacent to the network element, thefailure value including the first identifier and the second identifierrelatable to the failure of the first working path.
 21. The methodaccording to claim 20 further comprising the step of inserting thefailure value into an interrupt driven overhead byte of a protectionsignal for transmission over the mesh network for communication betweenthe interconnected network elements and the network element.
 22. Themethod according to claim 21 further comprising the step ofcommunicating the failure value in the overhead byte of the protectionsignal to help establish the first protection path after the failure hasbeen detected in the local working segment of the first working path.23. The method according to claim 22, wherein the protection signal isselected from the group comprising: a switch request, an acknowledgementof a switch request, a negative acknowledgement of a switch request, arevert back to working request, and an acknowledgement of a revert backto working request.
 24. The method according to claim 19, wherein thefirst identifier is a first byte of a pair of overhead bytes and thesecond identifier is a second byte of the pair of overhead bytes. 25.The method according to claim 19, wherein the first byte is selectedfrom one of a K1-K2 byte pair and the second byte is selected from theother one of the K1-K2 byte pair.
 26. The method according to claim 18further comprising the step of defining the protection routinginformation contained in the routing table when the N working paths ofthe path layer are established.
 27. The method according to claim 26further comprising the step of providing the protection routinginformation contained in the routing table by a controller associatedwith the network element.
 28. The method according to claim 26, whereinthe protection routing information is distributed in the path layer ofthe mesh network.
 29. The method according to claim 15 wherein a secondprotection path is associated with the N working paths to provide a M:Nshared mesh protection scheme.